Recently, semiconductor devices have become more integrated, and the structure of semiconductor elements has become more complicated. In addition, the number of layers in multilayer interconnections used for a logical system has been increased. Therefore, irregularities on the surface of the semiconductor device are increased, so that the step height on the surface of the semiconductor device becomes larger.
When the irregularities of the surface of the semiconductor device are increased, the following problems arise. The thickness of a film formed in a portion having a step is relatively small. An open circuit is caused by disconnection of interconnections, or a short circuit is caused by insufficient insulation between the layers. As a result, good products cannot be obtained, and the yield is reduced. Further, even if a semiconductor device initially works normally, reliability of the semiconductor device is lowered after a long-term use. At the time of exposure in a lithography process, if the irradiation surface has irregularities, then a lens unit in an exposure system is locally unfocused. Therefore, if the irregularities of the surface of the semiconductor device are increased, then it is difficult to form a fine pattern on the semiconductor device.
Thus, in the manufacturing process of a semiconductor device, it is increasingly important to planarize the surface of the semiconductor device. The most important one of the planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) therein is supplied onto a polishing surface such as a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing surface so that the substrate is polished.
Conventionally, such a polishing apparatus has a polishing table having a polishing pad (or fixed abrasive) attached to the upper surface thereof, and a top ring for holding a substrate (object to be polished) such as a semiconductor wafer. A polishing liquid containing abrasive particles is supplied from a nozzle onto the polishing pad and retained on the polishing pad. The polishing pad (or fixed abrasive) on the polishing table constitutes a polishing surface. During operation, the top ring exerts a certain pressure to press the substrate against the polishing surface of the polishing table, and the surface of the substrate is therefore polished to a flat mirror finish while the top ring and the polishing table are rotating. The polishing liquid comprises abrasive particles such as silica particles, and chemical solution such as alkaline solution in which the abrasive particles are suspended. Thus, the substrate is chemically and mechanically polished by a combination of a mechanical polishing action of abrasive particles in the polishing liquid and a chemical polishing action of chemical solution in the polishing liquid.
When the polishing process is finished, the polishing capability of the polishing pad is gradually deteriorated due to a deposition of the abrasive particles and ground-off particles removed from the substrate, and due to changes in the characteristics of the surface of the polishing pad. Therefore, if the same polishing pad is used to repeatedly polish the substrates, the polishing rate of the polishing apparatus is lowered, and the polished substrates tend to suffer polishing irregularities. Therefore, it has been customary to condition the polishing pad according to a process called “dressing” for regenerating the surface of the polishing pad.
In order to dress the surface of the polishing pad which has been deteriorated by polishing, a dressing apparatus having a dressing member is provided adjacent to the polishing table. In the dressing operation by the dressing apparatus, the dressing member fixed to a dresser head is pressed against the polishing pad (polishing surface) of the polishing table, and the dresser head and the polishing table are rotated relatively to each other for thereby bringing the dressing member in sliding contact with the polishing pad (polishing surface). Thus, the polishing liquid containing abrasive particles and the ground-off particles attached to the polishing surface are removed, and planarization and regeneration of the polishing surface are conducted. The dressing member generally comprises a dressing surface on which diamond particles are electrodeposited, and the dressing surface is brought into contact with the polishing surface.
In dressing of the polishing surface of the polishing table by the above dressing apparatus, there are two dressing methods. In one method, dressing of the polishing surface is conducted simultaneously with polishing of the substrate. In the other method, dressing of the polishing surface is conducted between polishing of the substrates, i.e. before or after polishing of the substrate. In both of the dressing methods, because the polishing surface is slightly scraped off by a dressing operation, if a dressing load applied to the polishing surface by the dressing member is large, then the service life of the polishing pad (or fixed abrasive) is shortened, resulting in an increase in cost. Therefore, there has been a demand for reducing the dressing load to minimize an amount of material to be removed from the polishing surface in the dressing operation.